Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C263/00—Preparation of derivatives of isocyanic acid
  • C07C263/18—Separation; Purification; Stabilisation; Use of additives
  • C07C263/20—Separation; Purification
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C263/00—Preparation of derivatives of isocyanic acid
  • C07C263/04—Preparation of derivatives of isocyanic acid from or via carbamates or carbamoyl halides

Definitions

• the invention relates to a process for the preparation of organic polyisocyanates by thermal cleavage of the carbamic acid esters on which they are based.
• N-substituted urethanes can be split thermally in the gas phase or in the liquid phase into isocyanates and alcohol [AW Hofmann, Ber. German Chem. Ges. 3 , 653 (1870); H. Schiff, Ber. German Chem. Ges. 3 , 649 (1870)].
• isocyanate follow-up reactions can be suppressed by short residence times.
• the molten carbamic acid ester is passed along the inner wall of a tubular reactor in the presence of small amounts of an auxiliary solvent, the high-boiling by-products formed and the auxiliary solvent are discharged as bottom product and that of isocyanate and Alcohol existing cracked gases removed overhead and separated by fractional condensation.
• auxiliary solvents Since only small amounts of auxiliary solvents are used in this process, ie the carbamic acid esters are subjected to thermolysis almost undiluted, the formation of highly viscous polymeric by-products cannot be avoided.
• the isocyanate taken off at the top is always contaminated by carbamic acid esters as a result of partial recombination with the alcohol also taken off at the top.
• a polar liquid whose dielectric constant is above 25 ° C and whose boiling point is at least 10 ° C above the boiling point of the alcohol on which the carbamic acid ester to be cleaved is based is used as the solvent or solvent mixture.
• a solvent with a boiling point or range of 1013 mbar at 30 ° C. to 200 ° C. selected from the group of aliphatic, cycloaliphatic or araliphatic hydrocarbons, aliphatic ethers or any mixtures of such solvents.
• Isooctane, cyclohexane, toluene and / or tert-butyl methyl ether are particularly preferred as extractants.
• the carbamic acid esters to be used in the process according to the invention are compounds or mixtures of compounds of the formula R1 (NHCOOR2) n in which R1 for an optionally inert aliphatic hydrocarbon radical with a total of 4 to 18 carbon atoms, an optionally inert substituent-containing cycloaliphatic hydrocarbon radical with a total of 6 to 25 carbon atoms, an optionally inert substituent-containing araliphatic hydrocarbon radical with a total of 7 to 25 carbon atoms or an optionally inert aromatic substituent Hydrocarbon radical with a total of 6 to 30 carbon atoms, R2 for an aliphatic hydrocarbon residue with 1 to 18 carbon atoms, a cycloaliphatic hydrocarbon residue with 5 to 15 carbon atoms, an araliphatic hydrocarbon is a radical of 7 to 10 carbon atoms or an aromatic hydrocarbon radical of 6 to 10 carbon atoms, and n represents an integer from 2 to 5, with the proviso that the alcohols R2-OH corresponding
• R1 represents an aliphatic hydrocarbon radical with a total of 4 to 12, in particular 6 to 10 carbon atoms, a cycloaliphatic hydrocarbon radical with 6 to 15 carbon atoms, a xylylene radical or an aromatic hydrocarbon radical which may have methyl substituents and / or methylene bridges and has a total of 7 to 30 carbon atoms
• R2 represents an aliphatic hydrocarbon radical having 1 to 6, in particular 1 to 4 carbon atoms, a cyclohexyl radical or a phenyl radical
• n represents an integer from 2 to 5.
• Typical examples of suitable carbamic acid esters are 1- (n-butoxycarbonylamino) -3,3,5-trimethyl-5- (n-butoxycarbonylamino-methyl) cyclohexane 1-methyl-2,4-bis (ethoxicarbonylamino) benzene 1-methyl-2,6-bis (ethoxicarbonylamino) benzene 1,10-bis (methoxicarbonylamino) decane 1,12-bis (butoxy carbonylamino) dodecane 1,12-bis (methoxicarbonylamino) dodecane 1,12-bis (phenoxy carbonylamino) dodecane 1,18-bis (2-butoxyethylcarbonylamino) octadecane 1,18-bis (benzyloxycarbonylamino) octadecane 1,3-bis (ethoxicarbonylamino-methyl) benzene 1,3-bis (methoxicarbonylamino) benzene 1,3
• Solvents which correspond to these criteria and are suitable for the process according to the invention as reaction medium are, for example, aliphatic sulfones such as diethyl sulfone, dipropyl sulfone, dibutyl sulfone, ethyl propyl sulfone; cyclic sulfones such as sulfolane, 2-methylsulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane; araliphatic sulfones such as methylphenyl sulfone, ethylphenyl sulfone; aromatic sulfones such as diphenyl sulfone, (4-methylphenyl) phenyl sulfone; aromatic nitro compounds such as nitrobenzene, 2-nitrotoluene, 3-nitrotoluene), 4-chloronitrobenzene; and mixtures of such compounds.
• Particularly suitable extraction agents are aliphatic or cycloaliphatic hydrocarbons or aliphatic ethers which have a boiling point between 30 ° C. and 200 ° C., preferably 30 ° C. to 150 ° C., at 1013 mbar.
• n-hexane, i-octane, gasoline corresponding to the definitions mentioned are suitable Fractions, cyclohexane or methylcyclohexane or aliphatic ethers with at least 4 carbon atoms, preferably 4 to 12 carbon atoms, for example diethyl ether, isomeric butyl ether, tert-butyl methyl ether or n-heptyl methyl ether.
• Aromatic hydrocarbons such as benzene, toluene or xylene are also suitable, but less preferred.
• the aliphatic or cycloaliphatic hydrocarbons mentioned by way of example are the particularly preferred extraction agents. Any mixtures of the extractants mentioned by way of example can of course also be used.
• the process according to the invention is generally carried out by adding the carbamic acid ester to be cleaved, optionally with the addition of up to 10 mol%, preferably up to 1 mol%, of a catalyst as at least 25% by weight, preferably at least 40% by weight. -% solution in a serving as a reaction medium solvent or solvent mixture of the above type at a pressure of 0.001 to 5 bar in a thin layer along the inner wall of a tube heated to temperatures of 150 ° C to 400 ° C along.
• the residence time of the carbamic acid ester in the reaction tube is kept very short in order to suppress side reactions, and the cleavage products are rapidly removed from the reaction zone together with at least part of the solvent used as gaseous products and are passed through two suitably temperature-controlled dephlegmators selectively condensed so that a fraction consisting mainly of alcohol and a fraction consisting mainly of isocyanate and solvent, which optionally contains the isocyanatourethanes and / or carbamic acid esters formed by incomplete cleavage or recombination, are obtained.
• reaction tubes suitable for the process according to the invention can be constructed in very different ways. They only have to be able to be operated in such a way that the carbamic acid esters fed into the tube can be distributed in a thin layer on the heated inner wall of the tube and the gaseous and / or liquid fission products can be removed from the reaction tube.
• the distribution of the fed carbamic acid esters on the inner wall of the tube can be done in vertical tube reactors without the use of special devices, provided that the carbamic acid ester to be split or its solution in a solvent is evenly applied to the tube wall using a suitable device, e.g. a nozzle. However, it can also be accomplished with the aid of a mechanical agitator or similar devices. In non-vertical tubular reactors, the use of an agitator or other suitable device is necessary in most cases.
• the agitators used to produce or improve the liquid film can advantageously also be used to transport the material located on the tube wall, be it that they inhibit the downward flow movement of the liquid film, or that they feed the fed in oblique or horizontal reactors, convey carbamic acid esters dissolved in solvents and / or their decomposition products across the gap zone to the end of the tube.
• the high-boiling by-products are discharged, if appropriate together with part of the solvent or solvent mixture used as the cleavage medium, as the bottom product.
• Suitable gap reactors are e.g. B. glass, quartz or metal tubes working as falling film evaporators, equipped with screw-type agitators, possibly tapering towards the end, tube reactors or conventional thin-film evaporators in various embodiments.
• screw-type agitators possibly tapering towards the end, tube reactors or conventional thin-film evaporators in various embodiments.
• thin-film evaporators equipped with mechanical stirrers have proven to be particularly cheap.
• the process according to the invention proceeds properly if there is a continuous depletion of fed carbamic acid esters in the liquid film coming down and no or very little starting material arrives at the end of the gap zone.
• the fiction Moderate processes for the thermal cleavage of carbamic acid esters can of course also be carried out in such a way that the carbamic acid esters introduced are only very incompletely cleaved by taking off as fraction II a product which contains predominantly or at least partially isocyanatourethanes and / or carbamic acid esters.
• fraction II formed during the thermal cleavage of carbamic acid esters which predominantly contains the polyisocyanates to be prepared, but also contains residues of carbamic acid esters which are not or only partially cleaved, is subjected to an extraction in a second process step. If desired, fraction II can of course be diluted beforehand with other solvents of the type mentioned above.
• the isocyanate-containing fraction II is thoroughly mixed with an extracting agent of the type mentioned above which is liquid at room temperature, the extracting agent being 0.1 to 25 times, preferably 0.5 to 5 times, based on the fraction II to be extracted Amount of weight is used.
• the fraction II is mixed with the extracting agent generally within the temperature range from -20 ° C. to 150 ° C., preferably at 10 ° C. to 100 ° C.
• the formation of a two-phase system can also be promoted by cooling the mixture of fraction II with the extraction agent. For example, it is possible to mix at about 70 ° C to 100 ° C and then cool the mixture to a lower temperature, for example in the temperature range from 10 ° C to 40 ° C.
• the specifically lighter phase generally forms the main phase and the specifically heavier phase forms the secondary phase, the volume ratio largely depending on the amount of extractant used.
• the phase separation can be carried out by methods known per se, for example by draining the heavier phase, decanting, siphoning or other suitable phase separation methods.
• Part of the polyisocyanate to be obtained in pure form is then in the specifically lighter main phase.
• Other constituents of the specifically lighter phase are part of the solvent used as the cleavage medium and the majority of the extracting agent used.
• the specifically heavier phase consists mainly of the solvent used as the cleavage medium, the unreacted or only partially converted carbamic acid esters and the one not into the specifically lighter phase transitioned part of the polyisocyanate to be obtained.
• the specifically heavier phase can be subjected to one or more new extractions in the manner described.
• fraction II is mixed with the extractant and the subsequent phase separation, ie. H. the extraction of Fraction II, continuously using the usual, continuously operating countercurrent extraction apparatus.
• the result of the extraction is one or more, optionally to be combined, specifically lighter extract phases which contain the polyisocyanate to be obtained and a, as a rule homogeneous, second phase which contains predominantly unconverted or only incompletely converted carbamic acid esters.
• This second, specifically heavier phase can be returned to the cleavage reaction.
• the specifically lighter extract phases mentioned are worked up by distillation, the extracting agent generally being the fraction to be removed first by distillation.
• the polyisocyanates can also be separated from residual amounts of the solvent by distillation, with the polyisocyanate or as the cleavage medium Solvent used forms the distillation residue. It is preferred to use solvents of the type exemplified above which differ sufficiently in their boiling behavior from the polyisocyanate to be obtained that a proper separation is possible.
• the polyisocyanate to be obtained in the distillative workup of the specifically lighter extract phases represents the distillation residue.
• the distillative workup can also be carried out continuously using the known distillation apparatus.
• the polyisocyanates generally obtained as distillation residues can optionally be subjected to a further fine distillation. However, even without such fine distillation, the polyisocyanates obtained as distillation residues already have a degree of purity of more than 90% by weight in some cases.
• the yield after a first cycle means the actual yield obtained in the examples.
• the yield for continuous driving is based on the total amount of diisocyanate obtained by (1) recovering additional diisocyanate from the first cycle and (2) converting unreacted and partially reacted carbamic acid ester to product in subsequent decomposition publications.
• a cylindrical thin-film evaporator (effective length 300 mm; diameter 35 mm) is used as the fission reactor, which is equipped with a blade impeller made of metal, the movable blades of which extend to the wall of the thin-layer evaporator.
• a heated dropping funnel attached to the top of the thin-film evaporator is used to feed in the carbamic acid ester to be split.
• the discharge of non-evaporable reaction products takes place via a shut-off valve attached to the base of the thin-layer evaporator, the evaporable components of the reaction mixture are removed from the top of the thin-layer evaporator via a heated cross-flow cooler, on the upper end of which are two serpentine coolers connected in series, each with a removal base for the condensates .
• the fission apparatus is evacuated via a cold trap located behind the snake coolers by means of a rotary vane pump.
• the isocyanate-containing condensate obtained as fraction II during the cleavage reaction is brought to a temperature suitable for the extraction, if appropriate after addition of further solvent, and in a heatable flask with a bottom outlet, which is equipped with a glass-enclosed blade stirrer, a thermometer and a reflux condenser. extracted. To do this, it is mixed with the extractant and stirred intimately for 30 minutes. After standing for 10 minutes, the two phases formed can be separated, with the specifically heavier phase being one in some examples or several further extractions with fresh extractant. The specifically lighter phases are combined and, like the heavier phase remaining after the extractions, checked for their composition by means of HPLC.
• a solution of 285 g of 4,4'-bis (ethoxycarbonylamino) diphenylmethane (MDU) and 0.72 g of dibutyltin dilaurate in 300 g of sulfolane (dropping rate: 120 g / h) is added in 5 hours via the dropping funnel, which has been thermostated to 100 ° C a thin film evaporator heated with 270 ° C heat transfer oil.
• the cross-flow cooler which is attached overhead, is thermostatted to 200 ° C, the two coil coolers to + 50 ° C or -20 ° C.
• the pressure in the apparatus is 4 mbar during the cleavage.
• the gas mixture escaping overhead is fractionally condensed on the two coil coolers.
• fraction I composition: 74% by weight of ethanol; 26% by weight of sulfolane
• fraction II composition: 55.1% by weight of sulfolane, 28.1% by weight of 4.4
• MDI 'Diisocyanatodiphenylmethane
• MIU 4-ethoxycarbonylamino-4'-isocyanatodiphenylmethane
• MDU 4,4'-bis (ethoxycarbonylamino) diphenylmethane
• DI means urethane-free polyisocyanates, especially diisocyanate
• IU partially split product containing urethane and isocyanate groups, especially isocyanatourethane
• DU means unchanged starting material, especially diurethane.
• Fraction II is extracted four times with 500 g of cyclohexane at room temperature.
• the sulfolane phase after the last extraction contains 45.8 g MDI, 55.2 g MIU and 14.5 g MDU
• the collected extracts contain a total of 79.8 g MDI and 4.5 g MIU (the MDU content is below the detection limit).
• MDI 4,4'-diisocyanatodiphenylmethane
• Example 1 a solution of 290 g of 4,4'-bis (ethoxycarbonylamino) diphenylmethane (MDU) and 0.76 g of dibutyltin dilaurate in 300 g of sulfolane (dropping rate: 100 g / h) in a 270 ° C. solution within 6 hours hot heat transfer oil heated thin film evaporator thermolyzed.
• 66 g of fraction I composition: 94% by weight of ethanol; 6% by weight of sulfolane
• 510 g of fraction II composition: 59.9% by weight of sulfolane; 25.2% by weight of MDI; 11 , 8% by weight MIU and 3.1% by weight MDU.
• Example 1 a solution of 255 g of 2,4-bis (ethoxycarbonylamino) toluene (TDU) and 0.69 g of dibutyltin dilaurate in 75 g of sulfolane (dropping rate: 65 g / h) in a 270 ° solution within 5.5 hours C hot heat transfer oil heated thin film evaporator thermolyzed.
• the cross flow cooler which is attached overhead, is thermostatted to 150 ° C, the two coil coolers to + 30 ° C or -10 ° C.
• the pressure in the apparatus is 10 mbar during the splitting.
• fraction II composition: 34.9% by weight of sulfolane; 23.2% by weight of TDI; 35 , 3 wt .-% TIU (isomer mixture) and 6.7 wt .-% TDU).
• the collected extracts contain a total of 40.4 g TDI and 20.2 g TIU (mixture of isomers) (the TDU content is below the detection limit).
• 29.3 g of TDI, 72.4 g of TIU (isomer mixture) and 17.3 g of TDU are detected after the extraction has ended.
• TDI 2,4-diisocyanatotoluene
• Example 1 a mixture of 275 g of 1- (ethoxycarbonylamino) -3,3,5-trimethyl-5- (ethoxycarbonylaminomethyl) cyclohexane (IPDU), 0.70 g of dibutyltin dilaurate and 15 g of sulfolane is added over the course of 5 hours 150 ° C thermostatic dropping funnel (dropping speed: 60 g / h) is fed into the thin-film evaporator heated with 310 ° C hot heat transfer oil. The cross-flow cooler, which is attached overhead, is thermostatted to 150 ° C, the two coil coolers to + 20 ° C or -10 ° C. The pressure in the apparatus is 12 mbar during the splitting.
• IPDU 1- (ethoxycarbonylamino) -3,3,5-trimethyl-5- (ethoxycarbonylaminomethyl) cyclohexane
• IPDU 1- (ethoxycarbonylamino) -3,3,5-trimethyl-5- (
• fraction I composition: 94% by weight of ethanol; 6% by weight of sulfolane
• fraction II composition: 3.5% by weight of sulfolane; 45.9% by weight of IPDI; 47 , 0 wt .-% IPIU (mixture of isomers)
• IPDU carbamic acid ester
• IPDI 1-isocyanato-3,3,5-trimethyl-5- (isocyanatomethyl) cyclohexane
• Example 1 a solution of 240 g of 1,6-bis- (ethoxycarbonylamino) hexane (HDU) and 0.66 g of dibutyltin dilaurate in 85 g of sulfolane (dropping rate: 70 g / h) in one with 270 ° C hot heat transfer oil heated thin film evaporator thermolyzed.
• the cross-flow cooler which is attached overhead, is thermostatted to 150 ° C, the two coil coolers to + 20 ° C or -10 ° C.
• the pressure in the apparatus is 15 mbar during the cleavage.
• fraction I composition: 75% by weight of ethanol; 25% by weight of sulfolane
• fraction II composition: 27.9% by weight of sulfolane; 35.8% by weight of HDI; 36 , 6% by weight HIU
• HDU carbamic acid ester
• Fraction II is extracted four times at a temperature of 90 ° C with 160 g of isooctane. The collected extracts contain a total of 48.6 g HDI and 27.6 g HIU. After the extraction, 21.8 g HDI and 45.1 g HIU are detected in the sulfolane phase. With regard to the formation and isolation of 1,6-diisocyanatohexane (HDI), this results in a yield of 31.4% after a first cycle and a yield of 72.5% with continuous driving.
• HDI 1,6-diisocyanatohexane

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• 1989
  • 1989-05-10 DE DE3915181A patent/DE3915181A1/de not_active Withdrawn
• 1990
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